Influence of contamination on the thermal evaporation of a zinc melt

In a thermal evaporation process, the melt will become enriched with elements of a lower vapor pressure than the evaporating species. Industrial coating facilities used in the steel industry are expected to run for days where the enrichment can become a serious problem because the accumulation of contaminants will influence the evaporation process. In this paper, two cases were investigated; a zinc melt contaminated with aluminum and a zinc melt contaminated with lead. These elements were chosen because they are present in significant amounts in commercially available zinc ingots, and at the tested temperature aluminum is completely soluble in zinc while lead and zinc form an emulsion. The results show that for a zinc melt at a constant temperature, the zinc evaporation rate is inversely proportional to the atomic percentage of aluminum. The influence that lead contamination has on the evaporation rate is much smaller and at 40 atomic percentage lead the evaporation rate is still more than 95% of its original value.

► Al and Zn form an ideal solution so the evaporation rate is linear to the Zn atom %.
► Pb and Zn form an emulsion, so lead does not change the evaporation rate of zinc.
► The evaporation rate of this technique is not sensitive to oxides/insoluble elements.